During the last several years increasing cost and reduced availability of fuel has motivated many automobile manufacturers to produce more fuel efficient vehicles by not only reducing vehicle weight but by also reducing engine size or power relative to vehicle weight, thereby depriving motorists of accustomed vehicle performance, such as power for acceleration, hill-climbing, etc. To regain this performance and still retain fuel efficiency many automotive manufacturers have offered or considered offering vehicles with supercharger systems having displacement or turbodynamic blowers which are either mechanically driven by the engine crankshaft or turbine driven by the engine exhaust gases. Such systems though well-known have not met with great customer acceptance even though they had been satisfactorily used for years to maintain aircraft engine power with increasing altitude and to increase racing car speeds. Most of the automobile superchargers have been of the turbine driven-turbodynamic blower type commonly referred to as turbochargers; a few have been of the mechanically driven displacement blower type, e.g., vane or Roots blowers driven by gear arrangements, V-belts, etc.
The turbochargers in automobiles have been disappointing for several reasons. They have been relatively inefficient when operated outside of their range of maximum efficiency, have had slow response, have required relatively complicated and expensive controls to prevent overboost and engine damage, and have required large hot ducts in the already cramped and overheated engine compartments to direct exhaust gases to and from the turbine. Of these, the most unacceptable is probably slow response in boosting engine power for accelerating the vehicle from zero or low speeds.
The supercharger systems with mechanically driven displacement type blowers in automobiles have also been disappointing for several reasons. When used to deliver air to the engine full time over the full operating range of the engine, they have also been relatively inefficient and have caused rough low-speed engine operation. When used in combination with a bypass duct to deliver naturally aspirated air to the engine at low engine speeds and/or low engine power settings to improve rough low-speed engine operation, they have also been relatively inefficient and have had either slow response, as with turbochargers, or have had an overly fast response which caused a stepwise increase in engine power and therefore objectionable jerky vehicle operation. Further, supercharger systems with displacement type blowers have been subject to catastrophic failure due to engine backfire unless provided with special blowout valves.